New localities of Guignardia aesculi on leaves of seven Aesculus species(×carnea, flava, hippocastanum, ×neglecta, parviflora, pavia, turbinata) were recorded in Europe. The teleomorph was found on overwintered
leaves of A. hippocastanum in Slovakia. The occurrence of the Guignardia leaf blotch on A. hippocastanum and A. turbinata was also confirmed for the first time in South Korea. The causal fungus Guignardia aesculi and its conidial anamorph Phyllosticta
sphaeropsoidea and spermatial synanamorph Leptodothiorella aesculicola are described in detail and illustrated. Pathogenicity of the fungus was confirmed by inoculating horse chestnut leaves with conidia.